Portion of an electrical dimmer switch and cover plate



FIG. 1 is a front, bottom and right side perspective view of the design;

FIG. 2 is a front view thereof;

FIG. 3 is a right side view thereof;

FIG. 4 is a left side view thereof;

FIG. 5 is a top plan view thereof; and,

FIG. 6 is a bottom plan view thereof.

The back forms no part of the design. The broken line showing in the drawings is illustrative and forms no part of the claimed design. 

The ornamental design for portion of an electrical dimmer switch and cover plate, as shown and described. 